The Model Fuels Consortium (MFC) II (earlier post), led by Reaction Design, a leading developer of combustion simulation software, is developing software that its members can use to simulate accurately the formation of soot particulates. The software will be used to develop cleaner-burning engines and potentially fuels in advance of impending regulations in the US and Europe, which call for limits on the size and number of soot particles emitted by passenger cars.

Number- and size-based particle limits are being adopted to prevent the possibility of future filters meeting the particle mass limits but still allowing a high number of ultra-fine particles to pass. A paper published at the end of October by the National Association of Clean Air Agencies (NACAA) urging the US Environmental Protection Agency (US EPA) quickly to implement Tier 3 emission and fuel regulations noted that:

...ultra-fine (UF) particles have recently attracted significant scientific and medical attention. These are particles smaller than 0.1 µm and are measured as a number concentration.

...A study led by UCLA researchers has revealed that the smallest particles from vehicle emissions may be the most damaging components of air pollution in triggering plaque buildup in the arteries, which can lead to heart attack and stroke.

...Another study, published in the New England Journal of Medicine, linked exposure to diesel exhaust with asthma. The researchers recruited 60 adults with either mild or moderate asthma to participate in a randomized, crossover study. Each participant walked for 2 hours along a London street (Oxford Street) and, on a separate occasion, through a nearby park (Hyde Park). Detailed real-time exposure, physiological and immunologic measurements were taken.

Participants had significantly higher exposures to fine particles (less than 2.5 µm in aerodynamic diameter), UF particles, elemental carbon and NO2 on Oxford Street than in Hyde Park. Walking for 2 hours on Oxford Street induced asymptomatic but consistent reductions in the forced expiratory volume in 1 second (FEV1) (up to 6.1%) and forced vital capacity (FVC) (up to 5.4%) that were significantly larger than the reductions in FEV1 and FVC after exposure in Hyde Park...The effects were greater in subjects with moderate asthma than in those with mild asthma...The changes were associated most consistently with exposures to UF particles and elemental carbon.

—“Cleaner Cars, Cleaner Fuel, Cleaner Air”

In Europe, Euro 5b/6 legislation introduced a particle number (PN) emission limit (6.0×1011/km) in addition to the mass-based limits for compression ignition engines. A particle number emission limit for gasoline vehicles—spurred by the adoption of gasoline direct injection engines—is to be defined by 1 September 2014.

The California Air Resources Board (ARB) is also considering adding a solid particle number (SPN) limit to the upcoming LEV III standards in California; LEV III harmonization with forthcoming US EPA Tier 3 regulations is likely.

Soot formation occurs when fuels don’t fully combust, and recent studies show that soot particles smaller than 100 nanometers can be especially harmful to human health. While engine exhaust regulations of the past decade have been largely focused on limiting the total amount of soot emissions, just last month the European Union extended its Euro5 regulation to control the actual number of particles, due to these known health effects. The MFC and Reaction Design have been working proactively to develop soot modeling approaches that help reduce these harmful emissions, as we anticipate that more regulations will follow with increasingly strict limits on particle size and number.

—Ellen Meeks, vice president of product development at Reaction Design

Unlike current methods that rely on empirical data to determine the amount of soot that an engine will produce, the MFC builds on fundamental scientific data accumulated over a decade of combustion kinetics research conducted by Reaction Design and others.

As part of the effort, Reaction Design engaged the University of Southern California to measure soot particle size and number from specific fuel molecules under controlled conditions, Meeks said.

With these software models and tools, MFC members will be able to accurately simulate the formation, agglomeration and reduction of soot particles with diameters from nanometers to microns in size. Using this predictive model of soot behavior, designers will be able to see the effects of changing engine parameters long before they commit to building a costly prototype.

The Consortium gathered 14–15 November in San Diego to discuss the latest findings and the next phase of project development. The soot model will be made available to current members of the MFC in December 2011. Interested companies may apply for membership and receive exclusive access to this model and other MFC data.

Meeks said that the MFC is extending for a year further to refine the soot model and test it more directly in engine simulations.

Automakers face a number of compliance issues like CAFE and Euro5+ that add to the complexity of engine design and lengthen the design process. MFC members recognize the importance of science-based soot modeling, because it can predict behavior, meaning we can test new designs on a computer rather than a physical prototype. This can shave days, weeks or months from a design cycle to get cleaner cars more quickly on the road.